One of the most difficult, yet critical, tasks that must be surmounted when building an internetwork is the selection of a routing protocol. As the preceding sections indicate, a rich palette of options await the prospective internetwork architect. Although the preceding overviews should help you to differentiate among the various classes of dynamic routing protocols, this is just the beginning. You still need to select a specific routing protocol, or protocols, from the variety that may be available in each class.
One of the best ways to start narrowing down the list of potential protocols is by evaluating each protocol's performance characteristics relative to projected requirements. Unlike hardware, you can't just compare routing protocols' packets-per-second or bandwidth ratings. They don't exist! Instead, you should look at how effectively each protocol performs the various tasks that support internetworking.
Two of the most important of these tasks are convergence and route calculation. The remaining sections of this chapter examine each of these concepts in more detail and should adequately prepare you for the more detailed examinations of individual protocols in the following chapters.
Note Of course, many other performance attributes must be considered, including maximum network diameter and how well a given protocol accommodates heavy traffic loads. Such characteristics, however, tend to be more applicable to specific protocols than to the three classes of dynamic routing protocols identified earlier in this chapter. As such, these performance characteristics are examined individually in Part III.
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